Grain structure and texture evolution during friction stir welding of thin 6016 aluminum alloy sheets

A “stop-action” technique was employed to study the grain structure and texture development during friction stir welding of thin 6016 aluminum sheets. The microstructural evolution ahead of the tool pin was found to be a complex process involving geometrical effects of strain as well as simultaneous development of continuous and discontinuous recrystallizations. At the circumference of the pin, the material flow was shown to be governed by the simple shear deformation induced by the rotating pin, which led to the formation of a pronounced {1 1 2}<1 1 0> simple shear texture. Beyond the pin, the material experienced additional hot deformation, possibly caused by the influence of the tool shoulder, and limited static annealing during the weld cooling cycle. As a result, a well-recrystallized grain structure having a characteristic {1 0 0}<1 0 0> cube texture finally developed in the stir zone.